Your hygrometer isn't reading properly, so you need to calibrate it. You can use the old salt/water/jar method, but if the amount of salt, or the salt/water ratio isn't right, the results will be off. How can you be sure that your hygrometer will be set properly? Use the Boveda 1-Step 75% Calibration Kit.
All you need to do is to place your hygriometer in the bag included in the kit, along with the provided 75% humidity pack. Let it sit for 24 to 36 hours and check your hygrometer. If it reads 75%, you're good to go. Otherwise, adjust it until it reads 75%. Simple, no-muss, no-fuss! Save more when you buy a brick of 12!